docs: def sig_encode(r, s):
      """Serialize ECDSA signature data into GPG S-expression."""
      r = util.assuan_serialize(util.num2bytes(r, 32))
      s = util.assuan_serialize(util.num2bytes(s, 32))
      return b'(7:sig-val(5:ecdsa(1:r32:' + r + b')(1:s32:' + s + b')))'